Please source where in NEH or other non-VA DEQ standard engineering hydrologic documents that require to adjust the HSG by atleast 1 factor when disturbing soils or working with disturbed soils as described in GM 5.301.D.1 & 5.302.D.2.

It is not found in the state regulations. The state regulations specifically state in 9VAC25-870-66.E "all pervious lands on the site shall be assumed to be in good hydrologic conditions in accordance with the US Dept of Ag NRCS standards, regardless of conditions existing at the time of computations."  In otherwords, despite how disturbed the conditions are, it does not give leeway for predevelopment to downgrade the runoff CN to poor. Post development may use "poor" pervious conditions due to disturbance if engineer judges so.

NRCS has hydrologic conditions already assigned for poor and good conditions stating that "Poor=Factors impair infiltration and tend to increase runoff; Good= Factors encourage average and better than average infiltration and tend to decrease runoff" It seems redundant to re-create NEH guidance and state that if lands are now disturbed (which is equivalent to impairing the infiltration ability of the soil using conditions of Poor) that instead of using historic standard practices (and whats used all over the country), that we should negate NEH and come up with new rules for hydrology. If new rules outside of the State Regulations are being created please provide the actual science/studies that supports this hydrologic adjustment (similarly to how NEH has done) for public commenting.

9VAC25-870-72.C also specifically states "NRCS OR other standard hydrologic & hydraulic methods shall be used..." This adjustment described in 5.301.D.1 & 5.302.D.2 is not standard with NRCS nor Rational Method, outside of the draft VA SWM HB please provide where is it standard in other hydrologic methods? If this is not actually standard, VA DEQ guidance to adjust disturbed soils is then going against State Regulations and creating new requirements outside the regulatory forum.

Also to note-Shouldn't the energy balance equation with the improvement factor adjustment already take into consider all these nuances with post development soils mixing?